Semiology of insular lobe seizures

After the early attempts of intra-operative electrocorticography and insulectomy in the 1950s, the notion of insular lobe seizures was largely forgotten for decades. It is only since the late 1990s that the recent technique of stereo-electroencephalography (SEEG) enabled preoperative diagnosis of insular origin seizures and thus gave rise to a renewed interest for this ill-defined electroclinical entity. Owing to the multiple functional roles of insula and its extensive connectivity with adjacent as well as distant brain structures, insular lobe seizures present with a combination or series of diverse subjective and objective symptoms. In this review, we summarize current knowledge on the semiology of insular origin seizures. The following two distinct forms of clinical presentation have been recognized: 1) Seizures with predominant insulo-perisylvian symptoms, most notably paraesthesia and cervico-laryngeal discomfort. The former typically involves a large/bilateral cutaneous territory and can be perceived as cold, hot, or painful sensations. The latter ranges from slight dyspnea to strong sensation of strangulation. Other symptoms include epigastric discomfort/nausea, hypersalivation, auditory, vestibular, gustatory, and aphasic symptoms. 2) Nocturnal hyperkinetic seizures with/without tonic elevation of upper limbs, masquerading as fronto-mesial seizures. Patients are usually not fully aware of their symptoms despite preserved contact and organized behavior to others. Ipsilateral eye blinking can be observed. These two patterns often occur in succession or simultaneously. This characteristic combination and progression of ictal symptoms orients us strongly towards an insular origin of seizure, a better understanding of which is a crucial key to further optimize modern SEEG strategy.